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Monday, August 25, 2014

Pain and Your Brain

Everyone is familiar with placebo effects.Just taking a pill can reduce pain you are
feeling, even if that pill has no active ingredients in it.Indeed, placebo effects help even when you
are taking an active ingredient.I know
that when I have a headache, taking some ibuprofen starts helping the pain
fairly quickly, even though it can take up to 30 minutes for the medication to
have an effect.

It is hard to study pain and placebo effects, because pain
is subjective.That is, you can’t know
whether people are experiencing pain unless you ask them.If people want sympathy, they might
exaggerate their report of pain.If they
want to avoid worrying their friends and relatives, they might minimize their
report of pain.

In addition, there may be many different psychological
systems involved in pain, and different treatments might influence these
systems in different ways.But, people
are only aware of the experience of pain.So, just focusing on the pain people are feeling does not help
researchers to tease apart the various ways that pain might be reduced.

An interesting paper by Tor Wager and Lauren Atlas in the
January, 2013 issue of Perspectives on
Psychological Science reviews evidence from brain imaging to tease
apart the influences of placebos on pain.

In order to study placebo effects, it is important to know
the regions of the brain that are involved in the sensation of pain.Wager and Atlas first review studies in which
participants were exposed to low-intensity and high-intensity heat in a
functional Magnetic Resonance Imaging (fMRI) study.The fMRI technique measures blood flow in the
brain and gives researchers information about areas of the brain that are
active in different situations.

If you are interested in the specific brain areas associated
with pain, check out
original paper.For now, what is
important is that these brain areas provide a way for researchers to explore
different effects of placebos.

Researchers have suggested that placebo effects might reduce
pain by activating opioid receptors in the brain.Opioid receptors are the ones that opiate
drugs (like morphine and codeine) activate.The brain has natural chemicals that activate these receptors, and that
helps minimize the experience of pain.For example, research has shown that placebo effects are reduced by
giving a person a chemical that blocks the activity of the opioid receptors.

One observation from these fMRI studies is that a region of
the midbrain (see the figure for a sense of where the midbrain is located) is
influenced by opioid receptors.This
area of the brain is affected by placebos.In addition, areas of the frontal cortex of the brain (located in the
brain above your eyes) is also related the strength of placebo effects.

Here is where it gets interesting.There are other areas of the frontal cortex
that are involved in your ability to control your thinking.Those areas of the brain are not involved in
placebo effects. However, researchers also know that if you distract yourself,
that can minimize the experience of pain.Presumably, distraction involves these brain areas that are associated
with thought control.

Based on these observations, other studies using brain
imaging show that distraction does reduce pain, but it uses different brain
regions than the areas involved in placebo effects.As a result, these two techniques can be
added together for a more powerful effect.That is, a combination of a placebo and distraction is better than
either one alone.

Finally, the pain-reducing opiate drugs involve some of the
same brain mechanisms of placebo effects and distraction, but they involve some
different ones as well.Which means that
in cases of the worst pain, a combination of all three effects can be more
powerful than any one alone.

You might wonder how you get a placebo effect when you have
taken a real drug.Remember, though,
that just the knowledge that you have been given a drug engages some pain
relief.That happens regardless of
whether that drug is a real painkiller or something inert.So, telling someone they are getting a pain
drug and then giving them that pain drug creates both a placebo effect and the
relief from the drug itself.

This work is interesting in two ways.First, it provides some new insight into how
placebo effects work.Second, it shows
how the maturing science of brain imaging can help science tease apart complex
mechanisms that would be hard to study without insight into what the brain is
doing.